Three situations are typically encountered in the connection and disconnection of electrical connectors in power distribution systems. The "loadmake" situation involves the joinder of male and female contact elements, one energized and the other engaged with a normal load. An arc of moderate intensity is struck between the contact elements as they approach one another and until joinder. The "loadbreak" situation involves the separation of such mated male and female contact elements, while they supply power to a normal load. Moderate intensity arcing again occurs between the contact elements from the point of separation thereof until they are somewhat removed from one another. The "fault closure" situation involves the joinder of male and female contact elements, one energized and the other engaged with a load having a fault, e.g., a short circuit condition. Quite substantial arcing occurs between the contact elements as they approach one another and until joinder, giving rise to the possibility of explosion and accompanying hazard to operating personnel.
The prior art teaches the use of materials which emit arc-quenching gas when subjected to arching, thus adequately dissipating the moderate intensity of arcs which occur during loadmake and loadbreak. The troublesome situation is fault closure, in which considerably more arc-quenching gas is required to extinguish the arc. In fact, gas generated pressures during fault closure may be fifty times greater than such pressures during loadmake.
Prior art efforts have reached a point wherein arcing during loadmake and loadbreak is satisfactorily accommodated.
As respects fault closure, certain prior art efforts have looked to the use of the aforementioned arc-quenching gas for assistance in accelerating contact elements into engagement, thus to minimize arcing time. While such prior art gas-assisted contact element engagement efforts have proved advantageous, need exists for continued improvement in connectors relying on arc-quenching gas-assistance in accommodating the fault closure situation through accelerated contact element engagement.
Typical prior art devices which are intended for fault closure use involve connectors each including a female contact assembly which comprises a female contact means and a piston which is movable between a first position and a second position. Gas pressure which is generated by arcing during fault closure accelerates the female contact toward the male contact, thus hastening contact engagement and decreasing the time duration of the arc. Such prior art devices are commonly referred to as "moving piston bushings". Examples are shown in Kotski U.S. Pat. No. 3,542,986 and in Stanger et al. U.S. Pat. Nos. 3,930,709 and 4,068,913, the latter two of which are commonly assigned herewith.
In Kotski U.S. Pat. No. 3,542,986, the female contact element is supported for axial movement by a piston against which arc-generated gas is applied. Thus, a piston assembly is disposed for unitary movement longitudinally within a conductive housing and includes such piston and female contact element and an insulative sleeve encircling the female contact element. The Kotski-type of moving piston bushing attains electrical continuity from the female contact element to the bushing terminal by means of a flexible electrical cable connected at one end thereof to the piston (which is in turn electrically connected to the female contact element) and at its other end to the bushing terminal.
In Stanger et al. U.S. Pat. No. 4,068,913, the Kotski-type device is modified by introduction of a valve transversely of the bore of the piston supporting the movable female contact element and the further introduction of a spring member exerting rearward axial force on the piston assembly and compressible upon forward piston assembly movement. The spring member serves to enhance rapid separation of the contact elements upon withdrawal of the male contact element from the bushing, as during loadbreak. Thus, upon separation of the male contact element from the female contact element, the piston assembly is spring-driven away from the existing male contact element.
In Stanger et al. U.S. Pat. No. 3,930,709, the development of which followed that of Stanger et al. U.S. Pat. No. 4,068,913, an improvement was made over both Kotski U.S. Pat. No. 3,542,986 and over Stanger et al. U.S. Pat. No. 4,083,383, in that the flexible cable which was connected to the piston and the bushing terminal was eliminated, in favor of a metallic louvered spring member encircling the piston and in electrically conductive relationship with both the piston and with conductive housing.
Other typical moving piston bushings of the prior art are shown in Westrom U.S. Pat. No. 3,945,699 and Fischer et al. U.S. Pat. No. 4,083,383. It is not believed necessary to discuss the devices of these two patents in detail.
All known prior art moving piston bushings entail movement of the piston from its first position to its second position during loadbreak. For reasons brought out in detail hereinafter, this piston movement is undesirable in that loadbreak stroke length is maximized.
It is therefore an important advantage of the present invention that it overcomes this undesirable feature of the prior art. This advantage is attained by the provision of means for retaining the piston in its first position except during fault closure.
The prior art moving piston bushings are not reliably reusable after fault closure. Another important advantage of the present invention is to provide a loadbreak bushing which is partially reusable after fault closure, by enabling reliable replacement of certain parts only, and not the entire device.
Among the important objects of the present invention are the provision of a moving piston device having the above advantages.